The oil and gas industry expends sizable sums to design cutting tools, such as downhole drill bits including roller cone rock bits and fixed cutter bits, which have relatively long service lives, with relatively infrequent failure. In particular, considerable sums are expended to design and manufacture roller cone rock bits and fixed cutter bits in a manner that minimizes the opportunity for catastrophic drill bit failure during drilling operations. The loss of a roller cone or a polycrystalline diamond compact (PDC) cutter from a fixed cutter bit during drilling operations can impede the drilling operations and, at worst, necessitate rather expensive fishing operations. If the fishing operations fail, sidetrack-drilling operations must be performed in order to drill around the portion of the wellbore that includes the lost roller cones or PDC cutters. Thus, during drilling operations, bits are pulled and replaced with new bits out of an abundance of caution, even though significant service could still be obtained from the replaced bit. These premature replacements of downhole drill bits are expensive, since each trip out of the well prolongs the overall drilling activity, and consumes considerable manpower, but are nevertheless done in order to avoid the far more disruptive and expensive process of, at best, pulling the drill string and replacing the bit or fishing and sidetrack drilling operations necessary if one or more cones or PDC cutters are lost due to bit failure.
In response to the ever-increasing need for downhole drilling system dynamic data, a number of “subs” (i.e., a sub-assembly incorporated into the drill string above the drill bit and used to collect data relating to drilling parameters) have been designed and installed in drill strings. Unfortunately, these subs cannot provide actual data for what is happening operationally at the bit due to their physical placement above the bit itself.
Data acquisition is conventionally accomplished by mounting a sub in the bottom hole assembly (BHA), which may be several feet to tens of feet away from the bit. Data gathered from a sub this far away from the bit may not accurately reflect what is happening directly at the bit while drilling occurs. Often, this lack of data leads to conjecture as to what may have caused a bit to fail or why a bit performed so well, with no directly relevant facts or data to correlate to the performance of the bit.
Recently, data acquisition systems have been proposed to install in the drill bit itself. For example, Baker Hughes Incorporated, assignee of the present invention, has developed a data acquisition system marketed under the trademark DATABIT®, embodiment of which are disclosed and claimed in U.S. Pat. No. 7,604,072; U.S. Pat. No. 7,497,276; U.S. Pat. No. 7,506,695; U.S. Pat. No. 7,510,026; and U.S. Pat. No. 7,849,934, each of which is assigned to the assignee of the present invention, and the disclosure of each of which is incorporated by reference herein in its entirety.
However, data reporting from these systems has been limited. Specifically, real-time data retrieval from a bit-mounted data acquisition system has been unavailable due to the lack of a robust technique for transferring data from the drill bit to the surface. As a consequence, data from such systems is, conventionally, only accessible when the drill bit has been tripped out of the well bore and the data acquisition system retrieved from the drill bit for data download. Such an approach limits the usefulness of information to the operator, who does not become aware of issues that may, if they could be addressed substantially in real time, enhance drilling performance and minimize the potential for damage to the drill bit.